1. Field of the Invention
The present invention relates to a webbing retractor which has a pretensioner mechanism for eliminating slackness of a webbing when a vehicle is in an emergency and a force limiter mechanism for limiting an amount of load applied to a vehicle occupant by the webbing to a fixed amount or less when a vehicle is in an emergency.
2. Description of the Related Art
There are webbing retractors with which a pretensioner mechanism, which eliminates slackness of a webbing when a vehicle is in an emergency, e.g., a collision, is provided.
In a webbing retractor having, among such a pretensioner mechanism, for example a so-called rack and pinion type pretensioner mechanism, a pinion is connected to a shaft for taking up the webbing. The pinion always rotates integrally with the take-up shaft. A substantially hollow cylinder is provided in the vicinity of the pinion. When a vehicle is in an emergency, gas is supplied to the cylinder.
A piston is movably provided within the cylinder. A fitting portion is formed at the lower portion of the piston. The fitting portion substantially fits into an inner wall of the cylinder. When a vehicle is in an emergency, the piston receives the gas pressure from below the fitting portion so as to be moved upward within the cylinder. A rack is provided at the upper portion of the piston. Due to moving upward of the piston, the rack meshes with the pinion such that the pinion is rotated in the direction in which the webbing is taken up. Thus, the webbing is taken up onto the take-up shaft when a vehicle is in an emergency to eliminate slackness of the webbing.
Further, the above-described webbing retractor is provided with a force limiter mechanism which limits an amount of load exerted upon a vehicle occupant by the webbing to a fixed amount or less when a vehicle is in an emergency.
Such a force limiter mechanism is provided with, for example, an energy absorbing member. The energy absorbing member is deformed by a load of a vehicle occupant onto the webbing when a vehicle is in an emergency, so that the take-up shaft is rotated in the direction in which the webbing is pulled out. Thus, when a vehicle is in an emergency, the webbing is pulled out from the take-up shaft, so that a load exerted upon a vehicle occupant by the webbing is limited to a fixed amount or less.
However, in such a webbing retractor, when the force limiter mechanism is operated, the take-up shaft is rotated in the direction in which the webbing is pulled out. Accordingly, the pinion is rotated in the direction in which the webbing is pulled out such that the piston is moved downward via the rack within the cylinder. The gas pressure within the cylinder (below the fitting portion) is increased to inhibit moving downward of the piston. Rotation of the take-up shaft via the rack and the pinion in the direction in which the webbing is pulled out is thereby inhibited, so that pulling out of the webbing is inhibited.
As illustrated in FIG. 12, a so-called force limiter load (which is equal to a load required for the webbing to be pulled out when a vehicle is in an emergency) is a load (a load shown by the portion A in FIG. 12) that a load by the gas pressure within the cylinder (the pressure which is increased due to moving downward of the piston) is added to a load required for the energy absorbing member to be deformed. Thus, there arises a problem that the degree of freedom of the setting of the force limiter load is narrowed.
In view of the aforementioned facts, an object of the present invention is to obtain a webbing retractor which can broaden the degree of freedom of the setting of a force limiter load.
A first aspect of the present invention is a webbing retractor which comprises a take-up shaft for taking up a webbing, a pretensioner mechanism which has a substantially hollow cylinder and a piston which is provided within the cylinder and with which a fitting portion which substantially fits into the inner wall of the cylinder is provided, and in which when a vehicle is in an emergency, gas is supplied within the cylinder and below said fitting portion such that the piston is moved upward due to the gas pressure to rotate the take-up shaft in the direction in which said webbing is taken up, and a force limiter mechanism having a deformable energy absorbing member in which when a vehicle is in an emergency, the energy absorbing member is deformed due to a load of a vehicle occupant upon the webbing such that the take-up shaft is rotated in the direction in which the webbing is pulled out to move the piston downward, and the webbing retractor comprising a gas passing portion which is provided at the piston and from which the gas can be discharged from below to above the fitting portion, and a closing device which is provided so as to correspond to a hole portion of the gas passing portion, substantially closes the gas passing portion under normal circumstances, maintains the state in which the gas passing portion is substantially closed when the piston is moved upward by the pretensioner mechanism, and which opens the gas passing portion when the piston is moved downward by the force limiter mechanism.
The webbing retractor of a first aspect of the present invention is provided with the pretensioner mechanism. When a vehicle is in an emergency, gas is supplied within the cylinder (below the fitting portion of the piston). As the gas passing portion of the piston is generally substantially closed by the closing device, gas within the cylinder is not discharged from the gas passing portion. Thus, the piston starts to be moved upward due to the gas pressure. When the piston is moved upward, the state in which the gas passing portion is substantially closed by the closing device is maintained. Thus, the piston continues to be moved upward such that the take-up shaft is rotated in the direction in which the webbing is taken up. Accordingly, when a vehicle is in an emergency, the webbing is taken up onto the take-up shaft such that slackness of the webbing is eliminated.
The webbing retractor of the first aspect of the present invention is provided with the force limiter mechanism. When a vehicle is in an emergency, the energy absorbing member is deformed by a load of a vehicle occupant upon the webbing such that the take-up shaft is rotated in the direction in which the webbing is pulled out. Accordingly, when a vehicle is in an emergency, the webbing is pulled out from the take-up shaft such that an amount of a load exerted on a vehicle occupant by the webbing is limited to a fixed amount or less.
In the force limiter mechanism, the take-up shaft is rotated in the direction in which the webbing is pulled out such that the piston is moved downward. When the piston is moved downward, the gas passing portion of the piston is opened by the closing device. Then, gas within the cylinder (below the fitting portion) is discharged from the gas passing portion. It is possible to prevent that moving downward of the piston is inhibited due to gas within the cylinder such that pull-out of the webbing is also inhibited.
A force limiter load (i.e., a load required for the webbing to be pulled out when a vehicle is in an emergency) can be determined by only a load required for the energy absorbing member to be deformed. Accordingly, the degree of freedom of the setting of the force limiter load can be broadened.
In the webbing retractor of the first aspect of the present invention, preferably the closing device is disposed on the fitting portion to substantially close the gas passing portion under normal circumstances. When the piston is moved upward by the pretensioner mechanism, the closing device is pushed upward by the fitting portion such that the state in which the gas passing portion is substantially closed is maintained. Further, when the piston is moved downward by the force limiter mechanism, the closing device is remained further upward than the gas passing portion, and the gas passing portion is thereby opened.
In accordance with the webbing retractor of the first aspect of the present invention, preferably, the closing device is generally disposed on the fitting portion of the piston such that the gas passing portion of the piston is substantially closed.
When the piston is moved upward by the pretensioner mechanism, the closing device is pushed upward by the fitting portion so as to be moved upward integrally with the piston. Thus, the state in which the gas passing portion is substantially closed by the closing device can be maintained.
When the piston is moved downward by the force limiter mechanism, a load of a vehicle occupant upon the webbing is transmitted via the take-up shaft to the piston. A descending speed of the piston is faster than a speed at which the closing device is moved downward due to free fall. Thus, the closing device is remained further upward than the gas passing portion such that the gas passing portion can be opened.
A closing device which substantially closes or opens the gas passing portion, for example in an electrical manner needs not to be used. As a result, it is possible to simplify the structure of the closing device.
Preferably the webbing retractor of the first aspect of the present invention further comprises a seal member which is provided so as to correspond to the gas passing portion. The seal member is interposed between the gas passing portion and the closing device so as to hermetically seal the gas passing portion. When the piston is moved upward by the pretensioner mechanism, the interposition of the seal member between the gas passing portion and the closing device is maintained so as to maintain the closure of gas passing portion. When the piston is moved downward by the force limiter mechanism, the interposition of the seal member between the gas passing portion and the closing device is released so as to open the gas passing portion.
In the above-described webbing retractor, the seal member is generally interposed between the gas passing portion and the closing device to seal the gas passing portion. Thus, moving upward of the piston can be started reliably.
When the piston is moved upward by the pretensioner mechanism, the seal member is moved upward integrally with the closing device and the piston. Accordingly, the state in which the seal member is interposed between the gas passing portion and the closing device is maintained. As a result, the state in which the gas passing portion is sealed by the seal member is maintained such that it is possible to maintain reliably moving upward of the piston.
When the piston is moved downward by the force limiter mechanism, for example, the closing device is remained further upward than the gas passing portion such that the state in which the seal member is interposed between the gas passing portion and the closing device is released. Then, the gas passing portion is opened. Gas within the cylinder can be still discharged from the gas passing portion.
A second aspect of the present invention is the webbing retractor of the first aspect comprising a closing device which has a cap capable of substantially closing the gas passing portion and a retainer disposed on the fitting portion so as to be able to inhibit the substantial closure of the gas passing portion by the cap from being released. In the closing device, when the piston is moved upward by the pretensioner mechanism, the retainer is pushed upward by the fitting portion to maintain the state in which said gas passing portion is substantially closed by the cap. When the piston is moved downward by the force limiter mechanism, the retainer is remained further upward than the fitting portion so as to release the state in which the gas passing portion is substantially closed by the cap.
In accordance with the webbing retractor of the second aspect of the present invention, the closing device includes a cap which can substantially closes the gas passing portion and a retainer which is disposed on the fitting portion such that it is possible to prevent the state in which the gas passing portion is substantially closed by the cap from being released. The retainer is generally disposed on the fitting portion and the cap substantially closes the gas passing portion.
When the piston is moved upward by the pretensioner mechanism, the retainer is pushed upward by the fitting portion. Thus, the state in which the gas passing portion is substantially closed by the cap can be maintained by the retainer.
When the piston is moved downward by the force limiter mechanism, a load of a vehicle occupant upon the webbing is transmitted via the take-up shaft to the piston. The descending speed of the piston is faster than a speed at which the retainer is moved downward due to free fall. Thus, the retainer is remained further upward than the fitting portion such that the state in which the gas passing portion is substantially closed by the cap is released. Then, the gas passing portion can be opened.
A device which substantially closes or opens the gas passing portion for example, in an electrical manner needs not to be used. Thus, it is possible to simplify the structure of the webbing retractor.
Preferably in the webbing retractor of the second aspect of the present invention, under normal circumstances or when the piston is moved upward by the pretensioner mechanism, an insertion member is inserted into the gas passing portion. Further when the piston is moved downward by the force limiter mechanism, the insertion member is discharged from the gas passing portion due to the gas pressure.
In the above-indicated webbing retractor, under normal circumstances or when the piston is moved upward by the pretensioner mechanism, because the insertion member is inserted into the gas passing portion, it is possible to further inhibit gas in the cylinder from being discharged from the gas passing portion. Thus, it is possible to prevent a decrease in a force required for the piston to be moved upward.
When the piston is moved downward by the force limiter mechanism, the insertion member is discharged from the gas passing portion due to the gas pressure. Thus, it is possible to discharge gas within the cylinder from the gas passing portion.
Preferably in the webbing retractor of the second aspect of the present invention, the gas passing portion has a bent portion and the insertion portion has elasticity. Further, the insertion member is bent and inserted into the bent portion under normal circumstances or when the piston is moved upward by the pretensioner mechanism.
In the above-indicated webbing retractor, under normal circumstances or when the piston is moved upward by the pretensioner mechanism, the insertion member having elasticity is bent and inserted into the bent portion of the gas passing portion. Thus, under normal circumstances or when the piston is moved upward by the pretensioner mechanism, the insertion member can appropriately close the gas passing portion.
Preferably in the webbing retractor of the present invention, friction is generated between the inner wall of the cylinder and the closing device when the piston in moved downward by the force limiter mechanism.
In the above-described state, when the piston is moved downward by the force limiter mechanism, friction is generated between the inner wall of the cylinder and the closing device. Thus, the closing device can be remained reliably further upward than the gas passing portion, and thus the gas passing portion can be opened reliably.
Even if friction is generated between the inner wall of the cylinder ad the closing device when the piston is moved upward by the pretensioner mechanism, the closing device is pushed upward by the fitting portion regardless of the friction. Thus, when the piston is moved upward by the pretensioner mechanism, the state in which the gas passing portion is substantially closed by the closing device can be still maintained.
In the webbing retractor of the present invention, when the piston is moved downward by the force limiter mechanism, the gas passing portion of the piston is opened by the closing device. Thus, it is possible to prevent that moving downward of the piston is inhibited due to gas within the cylinder such that pull-out of the webbing is also inhibited. The force limiter load can be determined by only a load required for the energy absorbing member to be deformed. Thus, the degree of freedom of the setting of the force limiter load can be broadened.
In accordance with the webbing retractor of the present invention, a closing device which substantially closes or opens the gas passing portion, for example in an electrical manner needs not to be used. Thus, it is possible to simplify the structure of the closing device.
In accordance with the webbing retractor of the present invention, friction is generated between the inner wall of the cylinder and the closing device when the piston is moved downward by the force limiter mechanism. Thus, the closing device can be remained further upward than the gas passing portion such that the gas passing portion can be opened reliably.